Effects of molybdenum and nickel additions on the structure properties of carburized and hardened low carbon steels

The effect of molybdenum and nickel on the microstructure and properties of low carbon steels in the carburized and hardened conditions were studied by means of optical microscopy, surface hardness and microhardness measurements, X-ray diffractometry and impact tests. It was found that molybdenum produces fine martensite and nickel has no effect in refining the size of martensite. Molybdenum with nickel is more effective than molybdenum without nickel in refining the size of martensite. Molybdenum and nickel enhance the formation of retained austenite in the case of carburized and hardened low carbon steels but nickel is more effective than molybdenum in enhancing the formation of retained austenite. Molybdenum improves and nickel reduces the maximum case hardness steels. The presence of nickel decreases the effect of molybdenum in the increment of maximum case hardness. Molybdenum and nickel both increase the core hardness but molybdenum is more effective than nickel in increasing the core hardness. Molybdenum with nickel is more effective in increasing the core hardness than molybdenum without nickel. Molybdenum and nickel both reduce the toughness of the core the steels. Nickel is more detrimental to toughness than molybdenum. (C) 2004 Elsevier B.V. All rights reserved.